The invention relates to a mechanical brake actuator for a shoe-drum brake, primarily intended to function as a vehicle parking actuator for maintaining the brake in operative condition when the vehicle is left unattended.
In one known form of such an actuator, a force input lever and strut member are pivotally interconnected and adapted for engagement respectively with outer end portions of the shoes of a drum brake, the actuator being expandible by application of force to the lever in order to apply the shoes to the brake drum for parking purposes in known manner. In this known actuator, portions of the lever and strut member are supported for sliding movement parallel to the brake backplate on surfaces fixed relative to the backplate, in order to react forces generated in these components in one direction perpendicular to the backplate. Such sliding movement can, however, be undesirable in that it tends adversely to affect the brake efficiency.
It is also known to provide a one-piece mechanism in the form of a strut which engages the webs of a pair of brake shoes, the strut being pivotable in order to expand the shoes and being supported on a surface of a fixed abutment member by way of a roller engaging a surface of said member adjacent the brake backplate.